1. Field of the Invention
The present invention relates to a pallet supply apparatus for a machine tool for performing an exchange of pallets between a plurality of rows of pallet supports and the machine tool. In particular, the invention relates to the pallet supply apparatus for at least one machine tool which apparatus is capable of supplying a desired pallet sequentially from a plurality of pallets on a plurality of pallet supports to a pallet exchange station immediately in front of the machine tool.
2. Description of the Related Art
As an example of a pallet supply apparatus for a machine tool, there is known an apparatus using a stacker crane, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 58-90451 base on U.S. Ser. No. 323,465 filed on 1981.11.20 which is now abandoned. The stacker crane is movable in a longitudinal direction between parts stocking structures. A fork of the stacker crane moves forward and backward at a right angle to the longitudinal direction of travel and is movable in the vertical direction (i.e., up and down). Thus, the stacker can remove, transfer, and deliver a pallet from and to different locations in the parts stocking structure. The structure of the stacker crane, however, must be able to bear the weight of a very heavy pallet during the lifting, lowering and transfer thereof, and accordingly, the stacker crane inevitably is large in size. Further, as support members must be provided in the forward and backward movement mechanism, the structure of the stacker crane is also complicated. Further, since a parts preparation station is usually located away from the parts stocking structure, a conveyor is necessary to connect the parts preparation station and the parts stocking structure, and this necessitates the use of a larger floor area.
A pallet supply apparatus is also known in which a fork type transfer vehicle moves between a pallet stacker arranged in a straight line and a group of machine tools, to remove and deliver pallets.
This pallet supply apparatus must comprise not only a plurality of means for performing the linear motion which enables the transfer vehicle to move along the pallet stacker, or to move the fork up and down and forward and backward, but also a means for rotating the vehicle between the minus 90 angle degrees and the plus 90 angle degrees corresponding to the pallet stacker position and the machine tool position respectively. Therefore, the moving mechanism is complicated and the transfer efficiency of pallets is unsatisfactory, and further, a large area is needed for rotating large pallets.